1. Field of the Invention
The present invention relates to a process for supplying nitrogen from an on-site plant.
2. Description of the Background
For a wide variety of industrial plants, it would be quite advantageous to produce nitrogen on-site. For example, it would be quite useful to produce a nitrogen stream on-site from chemical plants or steel plants where blanketing with an inert gas stream is often required, or in pulp and paper mills, where it is often necessary to pad chemical rail cars or tanks with nitrogen. In those plants where a huge amount of nitrogen is necessary, it is generally cheaper to connect the plant to a nitrogen pipeline fed by a nitrogen plant which could be remote from the said plants.
When the requirements are not too important, the customer usually has a tank which is regularly filled up with liquid or bulk nitrogen. This solution might be sometime expensive if only a small amount of gas is consumed. There are also cases where the purity required by the customer is either less than that of the bulk product or, on the contrary, is higher than that of the bulk product, e.g. for high technologies purposes such as semi-conductor industry or the like. There is presently no simple and cheap solution to achieve that goal.
In addition to the above, there is a need for some customers having on-site oxygen plants such as a PSA oxygen plant, for a small quantity of nitrogen which purity might be different from one customer to another or which purity might vary over the time on one site according to the customer's need. For example, some customers need a source of nitrogen of controllable purity or of variable flow rate, or both.
When a customer requires large amounts of oxygen, such as in excess of about 15 tons per day or more, oxygen is usually supplied on-site by an oxygen plant. At present, there are two principal commercial types of oxygen plants in operation. First, there are cryogenic plants, which utilize air liquefaction and distillation, and second, there are non-cryogenic plants based on pressure swing adsorption (PSA), vacuum swing adsorption (VSA), or a mixture of both. For a number of classical oxygen applications, a small quantity of nitrogen is also required for purge, transfer, blanketing, processing and/or other purposes.
Although new oxygen cryogenic plants can also be designed to produce a stream of nitrogen, the addition of an extra nitrogen capacity would be an advantageous feature, particularly if it can be at a different purity. However, existing oxygen cryogenic plants often have little or no nitrogen capability. Moreover, oxygen plants based upon PSA or VSA, do not allow for the recovery of a side nitrogen stream from the adsorption process.
Thus, in general, a need continues to exist for a means of supplying nitrogen from any industrial plant having a need therefor.